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mptcp: fix NULL ptr dereference on bad MPJ

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If an msk listener receives an MPJ carrying an invalid token, it
will zero the request socket msk entry. That should later
cause fallback and subflow reset - as per RFC - at
subflow_syn_recv_sock() time due to failing hmac validation.

Since commit 4cf8b7e48a ("subflow: introduce and use
mptcp_can_accept_new_subflow()"), we unconditionally dereference
- in mptcp_can_accept_new_subflow - the subflow request msk
before performing hmac validation. In the above scenario we
hit a NULL ptr dereference.

Address the issue doing the hmac validation earlier.

Fixes: 4cf8b7e48a ("subflow: introduce and use mptcp_can_accept_new_subflow()")
Tested-by: Davide Caratti <dcaratti@redhat.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Reviewed-by: Matthieu Baerts <matthieu.baerts@tessares.net>
Link: https://lore.kernel.org/r/03b2cfa3ac80d8fc18272edc6442a9ddf0b1e34e.1606400227.git.pabeni@redhat.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
This commit is contained in:
Paolo Abeni 2020-11-26 15:17:53 +01:00 committed by Jakub Kicinski
parent 69929d4c49
commit d3ab78858f
1 changed files with 2 additions and 3 deletions
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5
net/mptcp/subflow.c
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@ -543,9 +543,8 @@ create_msk:
fallback = true;
} else if (subflow_req->mp_join) {
mptcp_get_options(skb, &mp_opt);
if (!mp_opt.mp_join ||
!mptcp_can_accept_new_subflow(subflow_req->msk) ||
!subflow_hmac_valid(req, &mp_opt)) {
if (!mp_opt.mp_join || !subflow_hmac_valid(req, &mp_opt) ||
!mptcp_can_accept_new_subflow(subflow_req->msk)) {
SUBFLOW_REQ_INC_STATS(req, MPTCP_MIB_JOINACKMAC);
fallback = true;
}